strange bones rotation in the animations when exporting in FBX for unity
The problem was the quaternion rotation that was in conflict with the euler rotation (because i changed from quaternion rotation method to euler) and the only thing that I could do is to delete all the quaternion rotation keyframes and recalculate the roll of the bones in edit mode "shift+N" (recalculating the roll of all bones in the right way is important to export and mirror animations) because when blender is exporting in fbx it uses all the rotation keyframes and all the deforming/nondeforming bones deformations so sometimes you may see some graphics artifacts in animations so to avoid this there is an option in the armature tab when exporting called "only deform bones".